Method for the production of blister copper

ABSTRACT

The invention relates to a method to produce blister copper or high grade matte in a smelting reactor directly from a sulfidic copper concentrate containing material and/or finely ground copper matte, whereby oxygen-containing gas, copper concentrate and/or finely ground copper matte are fed into the reactor. According to the invention CaO and SiO 2  containing flux is fed into the smelting reactor along with oxygen-containing gas, copper concentrate and/or copper matte, and part of the copper in the concentrate and/or in the matte is oxidized in order to form a slag in which the CaO/SiO 2  ratio is higher than 1.5, and in which the copper content is in oxidized form, and in which the lime content calculated in a CaO+SiO 2 +FeO x =100 system is higher than 20%.

[0001] This invention relates to a pyrometallurgical method of producing blister copper in a smelting reactor, such as a suspension smelting furnace, directly from its sulfidic concentrate and/or finely ground copper matte.

[0002] A well-known method of the prior art is to produce raw copper or blister copper from a sulfidic concentrate in several stages, whereby the concentrate is smelted in a suspension reactor, such as a suspension smelting furnace, with air or oxygen-enriched air, which results in copper-rich matte containing 50-75 weight-% copper and slag. This kind of method is described in e.g. U.S. Pat. No. 2,506,557. Copper matte formed in a suspension smelting furnace is converted in for example a Pierce-Smith type converter or a flash converter into blister copper and refined further in an anode furnace.

[0003] The production of blister copper from sulfidic concentrate directly in one process step in a suspension reactor is economically viable within certain boundary conditions. The greatest problems involved in the direct production of blister include copper deportment to slag and the large amount of slag formed. The large amount of slag requires further treatment process step for copper recovery, which affects the economic feasibility of the process.

[0004] If the copper content of the concentrate is high enough, typically at least 37 weight-% copper, as for example at the Olympic Dam smelter in Australia, where the copper content of the concentrate normally exceeds 40 weight-%, it is possible economically to produce blister directly in one stage. When using the previously described concentrate the slag amount is moderate, but in order to produce blister, which has low sulphur content, less than 1 weight-% sulphur, the oxidation conditions must be selected so that the produced slag contains 15-25 weight-% copper.

[0005] Concentrate with a lower copper content can also be suitable for direct blister production, if it has an advantageous composition. For example, at the Glogow smelter in Poland, blister copper is produced from concentrate in one stage, since the iron content is low and the resulting amount of slag is not significantly high. The production of copper in one stage with the normal concentrates causes slagging of all the iron and other gangues. This type of method is described in the U.S. Pat. No. 4,030,915.

[0006] The FI patent 104838 describes a method to produce blister copper in a suspension reactor directly from a sulfidic copper concentrate, whereby the concentrate, flux and oxygen-enriched air are fed into the reactor. The cooled and finely-ground copper matte is fed into the suspension reactor along with the concentrate in order to bind the heat released from the concentrate and to decrease the amount of slag relatively, whereby the degree of oxygen enrichment of the air fed to the reactor is at least 50% oxygen.

[0007] This FI patent 104838 is however, limiting the process to areas, where the oxygen enrichment is higher than 50% oxygen and on the other hand the concentrate quality is limited to above 31% copper in a concentrate. The patent is limited to use both iron silicate slag (essentially free from calcia) and calcium ferrite slag (essentially free from silicate) depending on the concentrate quality.

[0008] The PCT patent application WO 00/09772 describes a method of smelting copper sulphide concentrate by oxygen-smelting the copper sulphide concentrate, and removing most of the iron in the copper sulphide concentrate into slag as well as removing part or most of the sulphur therein as sulphur dioxide SO₂, thereby obtaining copper from sulphide concentrate as white metal, nearly white metal matte or blister copper. According to the method the oxygen-smelting is carried out to produce; slag in which a weight ratio of CaO/(SiO₂+CaO) is 0.3 to 0.6 (CaO/SiO₂=0.43 to 1.5) and a weight ratio of Fe/(FeOx+SiO₂+CaO) is 0.2 to 0.5, and a white metal, nearly white metal matte, or blister copper, by adding SiO₂ material and CaO material to the copper sulphide concentrate as flux. The object of that PCT patent application WO 00/09772 is to provide a copper sulphide concentrate smelting process for producing white metal or blister copper with continuous oxidation of copper sulphide concentrate or matte at the temperature of 1300° C. or less, without magnetite complications, which is applicable for the treatment of copper sulphide concentrate or matte containing SiO₂, with less loss of copper to slag, capable of recovering copper content of slag by flotation, with high removability of arsenic, antimony and lead into slag, and with less erosion of refractories.

[0009] The PCT patent application WO 00/09772, however, limits the suitable slag composition area to a window, where the CaO/SiO₂ ratio in the slag is lower than 1.5 and where the silica content in the slag is relatively high, minimum being about 12.4% SiO₂ in the pure CaO—SiO₂—FeO_(x)) system (CaO=18.6%). As the lime content in the slag is increasing the silica content of the slag has to be increased, too, and the total slag amount increases accordingly. For example when the CaO/(CaO+SiO₂) ratio is 0.6 and the ratio Fe/(CaO+SiO₂+FeO_(x)) decreases from 0.5 to 0.2 the slag amount is more than doubled. The highest CaO/SiO₂ ratio is 1.5.

[0010] The object of the invention is to eliminate drawbacks of the prior art and to achieve an improved method to produce blister copper or high grade matte in a suspension reactor directly from a sulfidic concentrate and/or finely ground copper matte wherein both silica (SiO₂) and lime (CaO) bearing materials are also fed in order to form a slag, which is fluid at the temperature range of 1250-1350° C. The essential novel features of the invention are apparent from the appended claims.

[0011] According to the method a copper sulphide concentrate and/or copper matte with oxygen-containing gas is fed into a smelting reactor, such as a suspension smelting furnace, into which both silica (SiO₂) and lime (CaO) bearing materials are also fed in order to form a slag so that the CaO/SiO₂ ratio in the slag is higher than 1.5, and which slag is fluid at the temperature range of 1250-1350° C. Essential to the slag fluidity is that the slag also contains copper in oxidized form at least 6 weight percent.

[0012] The method of the invention is based on the fact that oxidized copper in slag fluxes effectively both magnetite and dicalcium silicate, which limits the applicability of the CaO—SiO₂—FeO_(x) slag in the copper smelting. In the oxidation conditions, where the sulphur content in copper is below 0.8 weight-%, part of the copper in the concentrate and/or in the finely ground matte is oxidized causing the fluxing effect, which allows the widening of the operation window, i.e. eliminates the limitations CaO/(CaO+SiO₂)=0.3 to 0.6 and Fe/(CaO+SiO₂+FeO_(x))=0.2 to 0.5 as set in the method of the PCT patent application WO 00/09772.

[0013] The method of the invention produces blister copper or high grade matte in a smelting reactor from a mixture of copper concentrate and/or matte as well as silicate containing material and lime containing material. The cooled and finely ground copper matte is fed into the smelting reactor in order to produce blister copper with lower than 1.0 weight-% sulphur and a relatively low amount of slag, in which the activity of lime is high in order to increase the slagging of arsenic and antimony, but in which the activity of silica is high in order to eliminate lead from the blister copper.

[0014] The finely ground matte fed into the blister furnace may be matte produced in any kind of known smelting furnace having a copper content of 60-78 weight-%. A single suspension smelting unit may be designed directly as a blister smelter depending on the copper content and composition of the available concentrates and on the amount of the finely ground matte.

[0015] The slag is treated further in a single-stage or preferably two-stage slag cleaning. The two-stage cleaning method includes either two electric furnaces or an electric furnace and a slag concentrating plant. If the slag is treated in a slag concentrating plant, the slag concentrate can be fed back into the smelting reactor. Blister copper goes for normal refining in an anode furnace.

[0016] If the production of the high-grade matte is carried out in a flash smelting furnace, the slag produced in the blister smelting stage can be preferably granulated and fed into the primary smelting furnace for copper recovery. The economy of this depends on the amount of the concentrate in the feed mixture and on the slag amount produced. The slag from the primary smelting furnace goes then to a normal single-stage slag cleaning or directly disposed (an electric furnace, a slag cleaning furnace or slag flotation) depending on the copper content of the slag.

[0017] The invention is further described in more detail with reference to following examples and to the appended drawings, where

[0018]FIG. 1 shows copper content of different slag types as a function of normalized oxygen partial pressure (T=1300° C.) in blister copper according to the example 1,

[0019]FIG. 2 shows the distribution coefficient of arsenic between slag and blister copper in different slag types as a function of the normalized oxygen partial pressure in blister copper according to the example 1,

[0020]FIG. 3 shows the distribution coefficient of lead between slag and blister copper in different slag types as a function of the normalized oxygen partial pressure in blister copper according to the example 1,

[0021]FIG. 4 shows the copper content of slag given in FeO_(x)+CaO+SiO₂=100 diagram according to the example 1,

[0022]FIG. 5 shows the distribution coefficient of arsenic between slag and blister shown in FeO_(x)+CaO+SiO₂=100 diagram normalized to (% Cu) in slag=20% according to the example 1,

[0023]FIG. 6 shows the distribution coefficient of lead between slag and blister shown in FeO_(x)+CaO+SiO₂=100 diagram normalized to (% Cu) in slag=20% according to the example 1, and

[0024]FIG. 7 shows the 200 cP viscosity temperature of the slag given in FeO_(x)+CaO+SiO₂=100 diagram normalized to (% Cu) in slag=15% according to the example 1.

EXAMPLE 1

[0025] Blister copper was produced in a suspension mini pilot smelting furnace in a series of tests, where the copper containing raw materials were finely grained copper matte (72.3 weight-% Cu, 3.4 weight-% Fe, 20.3 weight-% S) and copper concentrate (29.2 weight-% Cu, 33.7 weight-% S, 21.0 weight-% Fe). The mixture of copper matte and concentrate (kg matte)/(kg matte+kg concentrate)*100 was ranging between 50-100%. The feed rate was 100-200 kg/h. The oxidation degree of blister copper produced was controlled by the oxygen coefficient (Nm³ O₂/ton of feed), and the slag composition (CaO/SiO₂, Fe/SiO₂ in slag) was controlled by adding silica sand and lime to the feed. After each period, during which the process parameters were kept constant, the slag and blister were tapped out of the settler of the mini pilot furnace and the produced blister copper and slag was analysed. The average sulphur content of the blister was 0.2 weight-% sulphur (0.01-0.89% sulphur).

[0026] As an example results of one of the test periods is given as follows: Matte feed rate 89.7 kg/h Matte quality (3.4% Fe, 18.2% S, 0.26% As, 72.3% Cu 0.2% Pb) Concentrate feed rate 59.9 kg/h Conc. quality (20.9% Fe, 30.7% S, 5.1% SiO₂, 30.2% Cu 1.3% As, 0.11% Pb) Silica sand feed rate 0.5 kg/h Lime feed rate 10.3 kg/h Technical oxygen feed rate to concentrate burner 29.0 Nm³/h Air feed rate to concentrate burner 31.0 Nm³/h Oxygen enrichment 59.2% Oxygen coefficient 245.4 Nm³O₂/t Butane feed to reaction shaft and settler 3.03 kg/h in order to balance the heat losses Duration of test (feed on) 3h 10 mm Tapping temperature 1300° C. Quality of blister produced: Sulphur content 0.08% S Arsenic content 0.077% As Lead content 0.035% Pb Quality of slag produced: Copper content 18.3% Cu Lime content 19.3% CaO Silica content 7.6% SiO₂ Iron content 28.2% Fe Arsenic content 0.68% As Lead content 0.28% Pb CaO/SiO₂ (w-%/w-%) 2.54 Fe/SiO₂ (w-%/w-%) 3.71 CaO/(CaO + SiO₂) (w-%/w-%) 0.72 Distribution coefficient of Arsenic between slag and 8.8 blister Distribution coefficient of Lead between slag and 8.0 blister

[0027] The applicability of the method is further described based on the results of the test runs and FIGS. 1-7.

[0028]FIG. 1 shows copper content of different slag types as a function of normalized oxygen partial pressure (T=1300° C.) in blister copper. It can be seen that when the CaO/SiO₂ ratio (at a given Fe/SiO₂ ratio) of the slag increases the copper content of the slag decreases. For comparison the copper content of fayalite (iron silicate) slag is given in FIG. 1, too. Compared with fayalite slag the copper content at the same oxygen potential is much lower.

[0029]FIG. 2 shows the distribution coefficient of arsenic between slag and blister copper L_(As) ^((slag/Cu))=(% As in slag)/(% As in blister) in different slag types as a function of the normalized oxygen partial pressure in blister copper. It can be seen that when the CaO/SiO₂ ratio (at a given Fe/SiO₂ ratio) of the slag increases the distribution coefficient of arsenic, L_(As) ^((slag/Cu)), increases. For comparison the distribution coefficient of arsenic between iron silicate slag and blister copper is given in FIG. 2, too. Compared with fayalite slag distribution coefficient of arsenic L_(As) ^((slag/Cu)), the one of the CaO/SiO₂ slag is higher at the same oxygen potential showing the much higher ability to remove arsenic from blister.

[0030]FIG. 3 shows the distribution coefficient of lead between slag and blister copper L_(Pb) ^((slag/Cu))=(% Pb in slag)/(% Pb in blister) in different slag types as a function of normalized oxygen partial pressure in blister copper. It can be seen that when the CaO/SiO₂ ratio (at a given Fe/SiO₂ ratio) of the slag increases the distribution coefficient of lead, L_(Pb) ^((slag/Cu)), slightly decreases. For comparison the distribution coefficient of lead between calcium ferrite slag and blister copper is given in FIG. 3, too. Compared with calcium ferrite slag distribution coefficient of lead L_(Pb) ^((slag/Cu))), the one of the CaO/SiO₂ slag is higher at the same oxygen potential showing the higher ability to remove arsenic from blister.

[0031]FIG. 4 shows the copper content of slag given in FeO_(x)+CaO+SiO₂=100 diagram. The results are normalized to the temperature of 1300° C. and to the oxygen partial pressure of log PO₂=−4.5. It can be seen, that when operating with FeO_(x)+CaO+SiO₂+copper oxide slag at a constant oxygen partial pressure the copper content of slag is between 10-20%, when the CaO/SiO₂ ratio is higher than 1.5 and the CaO content in CaO+SiO2+FeO_(x) system is higher than 20%.

[0032]FIG. 5 shows the distribution coefficient of arsenic between slag and blister shown in FeO_(x)+CaO+SiO₂=100 diagram normalized to (% Cu) in slag=20%. The isodistribution lines based on the test results are also indicated. When the CaO/SiO₂ ratio is higher than 1.5, the distribution coefficient increases when the CaO content in the system increases.

[0033]FIG. 6 shows the distribution coefficient of lead between slag and blister shown in FeO_(x)+CaO+SiO₂=100 diagram normalized to (% Cu) in slag=20%. When the CaO/SiO₂ ratio is higher than 1.5, the distribution coefficient of lead increases, when the CaO content in the system is decreasing.

[0034] The viscosity of the slags in the pilot tests was low enough that they could be tapped out of the furnace through a normal tapping hole. In order to study the viscosity behavior of the slags more detailed viscosity measurements were carried out for some of the slags produced in the pilot tests. FIG. 7 shows the 200 cP viscosity temperature of the slag given in FeO_(x)+CaO+SiO₂=100 diagram normalized to (% Cu) in slag=15%. The 200 cP viscosity temperature increases when the CaO content of the slag is decreasing. Based on theoretical calculations the solid magnetite formation is limiting the usability of this kind of slag as shown with the dashed line in FIG. 7.

[0035] Now, the results in the FIGS. 1-7 indicate that the slag is fluid enough to be tapped out of the furnace, when the CaO/SiO₂ ratio of the slag is higher than 1.5 and that the CaO content of the slag calculated in FeO_(x)+CaO+SiO₂=100 is higher than 20% and when the copper content of the slag is higher than 8% Cu in the slag. 

1. A method to produce blister copper or high grade matte in a suspension smelting reactor directly from a sulfidic copper concentrate containing material and/or finely ground copper matte, comprising feeding oxygen-containing gas, copper concentrate and/or finely ground copper matte into the reactor, feeding CaO and SiO₂ containing flux into the smelting reactor along with oxygen-containing gas, copper concentrate and/or copper matte, and oxidizing part of the copper in the concentrate and/or in the matte is oxidized in order to form a slag in which the CaO/SiO₂ ratio is higher than 1.5, and in which the copper content is in oxidized form, and in which the lime content calculated in a CaO+SiO₂+FeO_(x)=100 system is higher than 20%.
 2. A method according to claim 1, wherein the copper content in the slag in oxidized form is at least 6 weight percent.
 3. A method according to claim 1 wherein the activity of lime in the slag formed is high in order to increase the slagging of arsenic and antimony.
 4. A method according to claim 1 wherein the activity of silica in the slag formed is high in order to eliminate lead from the blister copper.
 5. A method according to claim 1, wherein the method is carried out in a smelting unit using oxygen-containing gas.
 6. A method according to claim 1, wherein in that the method is carried out in a suspension smelting furnace. 